The invention is based on a priority application (DE 10031 843.6) which is hereby incorporated by reference. The present invention relates to an electric or opto-electric component with a packaging of plastic. Arranged in the packaging is at least one electric or opto-electric integrated circuit. Terminal leads for the connection of the circuit or of each circuit protrude from the package. The circuit or each circuit can be attached with the aid of the terminal leads by means of a base, for example, or by means of a soldered connection to a printed-circuit board and integrated into a circuit arrangement formed on the circuit board. The present invention also relates to a method for varying the impedance of a terminal lead of such an electric or opto-electric component.
Electric or opto-electric components of the type stated at the beginning are known from the prior art. The integrated circuit arranged in the packaging of such a component can be designed for a wide range of applications, for example for a storage element or a microprocessor. The arrangement and size of the terminal leads (so-called pins) of the components are largely standardized. Components of this kind are used in particular in circuit arrangements that operate relatively slowly or at a relatively low frequency. In high-speed applications with a processing speed of several Gb/s and in high-frequency applications of several GHz, the impedance must be controlled during operation, i.e. the impedance of the components of the circuit arrangement, the impedance of the printed conductors of the circuit arrangement, the impedance of the terminal leads and the impedance of the circuits must be of roughly the same magnitude. Different impedances could lead in high-speed and high-frequency applications to disruptive signal reflections in the circuits or in the circuit arrangement on the circuit board.
The impedance of the printed conductors on the circuit board, the other components arranged on the circuit board and the circuits can be set to a value that is roughly the same without any great effort. Their impedance is typically around 25 Ohms or 50 Ohms. Only the bonding connections (e.g. bonding wires) between the circuits and the terminal leads of the component, and the terminal leads themselves have a higher impedance differing from this.
To reduce disruptive signal reflections, it would be necessary to reduce the impedance of the terminal leads to the impedance of the circuit arrangement into which the component is integrated and to that of the circuits. In known components with a packaging of plastic, the impedance of the terminal leads cannot simply be varied or reduced, however, as the arrangement, size and spacing of the terminal leads relative to one another are set. In addition, reducing the impedance of the terminal leads to around 25 Ohms or 50 Ohms in known components by changing the arrangement, size or spacing of the terminal leads would only be possible, if at all, with extremely high production engineering demands. These high production engineering demands result for example from the fact that the distance between two terminal leads arranged adjacent to one another would be so small in the event of the impedance being reduced to 25 Ohms or 50 Ohms that the terminal leads would scarcely be manufacturable using conventional punching dies.
Electric or opto-electric components are known from the prior art with a packaging of ceramic or metal. In these components, the impedance of the terminal leads can be varied and reduced to the impedance of the circuit arrangement into which the component is integrated, and of the circuits. The manufacture of components with a ceramic or metal packaging is very time-consuming and expensive, however.
The object of the present invention, therefore, is to provide an option that is as simple and cheap as possible for varying, and in particular reducing, the impedance of terminal leads of an electric or opto-electric component with a packaging of plastic.
The invention achieves the above objective by utilizing a component of the type described and attaching at least one dielectric plate to at least one of the terminal leads.
If the equivalent circuit diagram of two terminal leads (so-called pins) of the component arranged immediately adjacent to one another is examined, this has inductances running in the longitudinal direction of the terminal leads and capacitances between terminal leads arranged adjacent to one another. The impedance of a terminal lead is proportional to the square root of the quotient of inductance and capacitance, i.e. the impedance of a terminal lead can be reduced by increasing the capacitance acting between two terminal leads. It is proposed according to the invention to increase the capacitance between the terminal leads by attaching at least one dielectric plate to the terminal leads. The capacitance can be varied by the choice of material and thus the dielectric constant of the dielectric plate and by varying the dimensions of the dielectric plate. The impedance of the terminal leads can be set to a desired value by a suitable choice of material and the dimensions of the dielectric plate.
It would be conceivable to attach the dielectric plates to the terminal leads outside the packaging. According to an advantageous development of the present invention, however, it is proposed that the dielectric plate or each dielectric plate is attached to the terminal lead or each terminal lead in the packaging. This prevents the dielectric plates from being inadvertently removed from the terminal leads, and the component according to the invention is easier to handle. In addition, the component according to this development can be manufactured particularly easily and cheaply, in that in the context of the production stage for production of the plastic packaging of the component, the circuit bonded to the terminal leads is encapsulated together with the dielectric plates fitting on the terminal leads in plastic.
According to a preferred form of embodiment of the present invention, it is proposed that the dielectric plate or each dielectric plate has a higher dielectric constant than the plastic of the packaging. The dielectric plate or each dielectric plate advantageously consists of ceramic, preferably of aluminium oxide (Al2O3).
According to another advantageous development of the present invention, it is proposed that the packaging is drawn laterally over the terminal leads. The terminal leads thus run inside the packaging horizontally in the first instance away from the circuit and then bend vertically downwards, to emerge finally from the packaging at the underside of the component. It is also conceivable that the terminal leads branch off once again from the vertical to the horizontal and only then emerge laterally from the packaging. In this development, it is crucial that the terminal leads run over the maximum possible area inside the packaging and are enclosed by plastic. The dielectric constant of plastic, which encloses the terminal leads over virtually their entire length, is greater than the dielectric constant of air, which in conventional components surrounds a large part of the terminal leads. The terminal leads of the component thus have a reduced impedance according to this development, even if no dielectric plates are attached to the terminal leads. The dielectric plates can be attached to the terminal leads at any point of the terminal leads, preferably inside the packaging.
To increase the capacitance between the terminal leads further, it is proposed according to a further preferred form of embodiment of the present invention that the surface of the dielectric plate or each dielectric plate facing away from the terminal leads is coated at least partly with a metal layer. According to this development, the terminal leads and the metal layer form a plate condenser to some extent with the dielectric plate arranged in between.
Two dielectric plates are advantageously attached to the terminal leads. One of the dielectric plates can be attached to the areas of the terminal leads running horizontally inside the packaging and the other dielectric plate can be attached to the areas of the terminal leads extending vertically downwards.
The use of a dielectric plate to vary the impedance of a terminal lead of an electric or opto-electric component is also proposed according to the present invention. The component has a packaging of plastic, at least one electric or opto-electric integrated circuit arranged in the packaging and several terminal leads protruding from the packaging for connection of the circuit or each circuit. To vary the impedance of the terminal lead, the dielectric plate is attached to the terminal lead.
As another way of achieving the object of the present invention, it is proposed starting out from the method of the type stated at the beginning that at least one dielectric plate is attached to at least one of the terminal leads.